Connecting strip



Aug. 13, 1957 P. VAN LEEUWEN 2,802,971

CONNECTING STRIP Filed Dec. 3, 1953 INVENTOR United States Patent GCONNECTING STRIP Pieter van Leeuwen, Hilversum, Netherlands, assignor,by

mesne ass1gnments, to North American Philips Compauy, Inc., New York, N.Y., a corporation of Delaware Application December 3, 1953, Serial No.396,017

Claims priority, application Netherlands December 5, 1952 8 Claims. (Cl.317-112) This invention relates to a connecting strip comprising aplurality of relatively insulated connecting members or contact membersand more particularly to a structural element of a contact bank forautomatic telephone systems or similar apparatus.

It is known to build up contact banks by stacking a plurality ofconnecting strips, each comprising a series of contact members which inmost cases project on each side from the edge of the strip. As a rule,the ends at one side of the strip are intended for securing the multiplecables and those at the other side for co-operation with a movablecontact member. The known connecting strips for this purpose are, inmost cases, formed by clampng a series of contact members betweeninsulating strips or, as is more usual, surrounding the series ofcontact members in a templet by casting or moulding with an insulatingplastic material, which is subsequently hardened. The connecting stripsthus obtained have the disadvantage that there are comparatively largetolerances as a result of the limited accuracy in working and inneraction of the insulating material, such as contraction in cooling. Notonly comparatively large tolerances in the spacing between the contactmembers of a strip are present but also deviations in the mutualpositions of the contact series of a plurality of connecting stripsassembled into a contact bank are unavoidable. A consequence of all thisis that a contact bank for a selector switch for automatic telephonesystems which comprises a determined number of contacts per layer islimited to a determined minimum sze since it is necessary that thewipers shall co-operate in the correct manner with the contacts of thebank at each stop position of the wiper carrier of the selector.Therefore, as a result of the said tolerances, the spacing between thecontact members cannot be so small as would be possible otherwise.

In the manufacture of known connecting strips comprsing fiat contactmembers use is commonly made of a series of contact members which areobtained in the correct mutual positions by punching a metal plate, andthe extremities of which are connected to a remaining portion of theplate. After the said coherent series of contact members has beenprovided in the connecting strip,the positions of the plate connectingthe extremities ofthe'contact member are cut away. This method has thedisadvantage that an important loss of material is involved.

The object of the invention is to provide a connecting ing of aplurality of connecting strips according to the invention to form acontact bank, it is possible either to adinit more contact members perseries with a given sze or to reduce the size of the strip when adetermined number of contact members per series is retained. This atordsthe advantage that in a contact bank for a selector built up from suchstrips more contacts can be wiped per unit time without increasing themass forces which occur when the wiper carrier is acceleratcd orstopped. This is very important, more particularly, in systems fordirect telephony, that is to say, telephone systems without registers.

According to the invention, the connecting strip is constituted by ametal supporting strip having a plurality of transverse grooves in whichpieces of metal wire projecting trom each side of the strip are centeredin an insulatng manner by means of at least one wire or ribbon offlexible insulating material, for exarnple nylon cord, extending in thedirection of the length of the supporting strip and under the successivepieces of wires, the pieces of wire and the insulating wire or rib bon,at their crossings, being inter-connected and connected to thesupporting strip with the use of an insulating adhesive.

Since the supporting strip is of metal for which a light weightaluminium that may be anodized is preferred, it may be manufactured withvery small tolerances. Furthermore, electric screening between thecontact members of the various strips is ensured automatically instacking a plurality of such connectng strips.

In order that the invention may be readily carried into effect, it willnow be described in detail with reference to the accompanying drawingshowing, by way of example, one embodiment thereof.

Fig. 1 is a plan view on a semi-circular connecting strip intended as astructural element for a contact bank of a rotary switch for automatictelephony.

Fig. 2 is a cross sectional view of this strip taken along the line IIIIof Fig. 1.

Fig. 3 shows part of a longtudinal section taken along the line IIIIIIof Fig. 1, and

Fig. 4 shows part of a longitudinal section taken along the line IVIV ofFig. 1.

The embodiment shown in the figures comprises a fiat aluminiumsupporting strip 1 which is semi-circular in shape. The strip 1comprises, on its upper side, a plurality of transverse grooves -2,which are directed towards the center of the circle and in which contactmembers are provided in the form of pieces 3 of metal wire which projectfrom each side of the strip.

For reasons which will be mentioned hereinafter, Fig. 1 shows threeseparate groups of pieces of wire, that is A, B and C, although thesupporting strip 1 as shown actually comprises only pieces of wire suchas those in group C.

The pieces of wire 3 are centered in an insulating mannr in thetransverse grooves 2 by the aid of two nylon cords 4 which extend in thedirection of the length of strip 1 at a small distance rom its edge.Said cords extend under the successive pieces of wire 3 in order 0 passon the upper side of the strip 1 to the subsequent transverse groove. Aninsulating adhesive 5 is provided for the mutual attachment of thepieces of wire 3 and the nylon cords 4 to the supporting strip 1 at thecrossing of a nylon cord and a piece of wire, that is to say in a groove2 (see Fig. 4). Use is preferably made of an ethoxylehe resn. The resin,after being provided, is cured in known manner, so that the pieces ofwire 3 and the portions of the nylon cords 4 surrounding them in partare extremely rigidly secured to the supporting strip 1. The nylon cordsextend over the upper side of the supporting strip 1 in longitudinalgrooves 6 in strip 1 having a depth smaller than that of the transverse.groo ves 2. Owirig to the provision in the grooves 6, of the cords 4,the cords 4 tlo not project above the profile of the supporting strip 1.-This is important,

sncc in stacking a plurality of such supportng strips the lower side ofone supportng strip bears directly upon the upper side of the subsequentstrip, so that the spacings between the series of pieces of wire in theconnecting strips are determined only by the thickness of the metalsupportng strips which can be obtained with very small tolerances.

The nylon cords 4, after having extended under all the wire pieces 3 inthe supportng strip return through the said pieces of wire to theirstarting point, the returning part (4) also being sccured at a crossingwith 2. piece of wire with the use of the insulating adhesive.

For the sake of clearness, Figs. 2 and 3 show .only a cross-section ofthe supportng strip 1, the pieces of wire 2 and the nylon cords 4 beingomitted.

Not all of the contact members 3 provided in the supportng strip 1 areshown in Fig. 1. Those which are shown are divided into three groups A,B and C,

whch show the contact members 3 in different stages of working. Asmentioned before, in the embodiment under consideration, all contactmembers provided in the supportng strip actually have the shape as shownfor group C.

The contact members 3 of groups A are constituted by rectilinear piecesof metal wire having the same sectional area throughout their length.

The contact members of groups B are consttuted by pieces of wire similarto those of group A, but with both ends flattenecl. Flat terminal parts7 and 8 located in the same plane are thus obtained. The parts 7 and 8may be formed before the pieces of wire are provided in the supportngstrip, but a simpler method is first to provide pieces of wire similarto those of group A and then to flatten all the ends of the pieces ofwire simultaneously in one operation.

The contact members in group C have acquired their ultimate shape bypunching the fiattened ends of pieces of wire (group B) secured in thesupportng strip 1 to the desired size with the use of a cuttng toolspecally made for this purpose. The correct mutual positiom'ng of thecutting tool and the connecting strip is obtained with the use ofcentering holes 11 provided in the extremitics of supportng strip 1.During the punching operation those extremities of the pieces of wirewhich are located on the inner side of the strip are formed into more orless rectangular flat contact surfaces 10 which are accurately spacedapart and which are intended to be engaged by a wiper in a selector, thecontact bank of which is built up trom such connecting strips. Theflattened ends 7 of the pieces of wire acquire by punching, as may beseen at 9, a profile whch facilitates the securing of connecting wiresthereto, for example, by solder- 1ng.

To ensure satisfactory contact between the contacts 10 and thecooperating wiper in a selector constituted by a plurality of theconnecting strips described, it may be desirable that the contactsurfaces should be provided with rare metal, for example palladium orsilver. This may be efrected by making those ends of the pieces of wirewhch, after being flattened, are punched into the desired shape of thecontact surfaces 10, wholly or in part from precious metal, for exampleeither by welding or securing in another manner 2. piece of preciousmetal wire t pieces of wire of base metal, for example of brass whichare to be arranged in the transverse grooves 2 or by providing therelative ends of the pieces of wire beforehand with a precious metal.

In the embodiment described, the supportng strip 1 is semi-circular inshape, so that the connecting strip may serve as a structural element ofa semi-cylindrical contact bank. However, the supportng strip mayalternatively have a different shape, for example, it may be rectilinearand thus constitute a structural element for a recti.liner contact bank.

strip being provided with a plurality of groves therein The connectingstrip according to the nvention may also be used for purposes other thanas a structural element for a contact bank. Thus, it may be used, forexample, as a distributing strip in telephone exchanges, as anassembling support for electric component parts in apparatus and as aconnecting strip for the windings for cnergizing an electrornagneticrelay. In relays the contact springs are in most cases clamped betweeninsulating spacers mounted on a connecting strip secured to the yoke andcomprise contact members for the energizing coils. Due to tolerances inthe thickness of the connecting strip, the contact springs are notalways correctly positioned relatively to the parts coupled to thearmature and moving the contact springs, so that after adjustment of thecontact springs is necessary. This disadvantage is obviated when usingthe connectingstrip according to the invention, the thickness of whichis reproducible in manufacture with a high accuracy.

While I have shown and described the preferred em bodiment of myinvention, it will be understood that the lattcr may be embodiedotherwise than as herein specifi cally illustrated or described and thatin the illustrated embodiment certan changes in the details ofconstruction and in the arrangement of parts may be made withoutdeparting from the underlying idea or principle of the invention Withinthe scope of the appended claims.

What is clairned is:

1. A combination of an elongated metal connecting positioned transverseto the direction of length of said strip, a relatively insulated pieceof bare metal wire having a circular cross-secton arranged in each ofsaid grooves, at least one flexible, insulating member in each of saidgrooves, said member extending along a plane surface of said strip inthe direction of length thereof and in said grooves and under saidsuccessive circular wires, and an insulating adhesive for connectingsaid circular wires and said insulating member at their points ofengagement.

2. A combination as set forth in claim 1 further comprsing anothergroove extending in a direction parallel to the direction of length ofsaid strip and having a depth smaller than that of said transversegrooves, and said insulating member bcing positioned in said othergroove.

3. A combination as set forth in claim 1 wherein said insulating memberaddtionally engages a portion of the top surface of each of said wiresand is secured at points of engagement therewith by said insulatingadhesive.

4. A combination as set forth in claim 1 further comprising twoinsulating wires, each extending adjacent to an edge of said connectingstrip, and said insulating wires being adapted to center said wirepieces in said transverse grooves.

5. A combination as set forth in claim 1 wherein said connecting stripis composecl of aluminum.

6. A combination as set forth in claim 1 wherein at least one end ofeach of said wires on the same side of said connecting strip isflattened.

7. A combination as set forth in claim 1 wherein said" insulatingadhesive is an ethoxylene resin.

8. A combination of an elongated metal connecting strip being providedwith a plurality of grooves therein positioned transverse to thedirection of length of said strip, a relatively nsulated piece of baremetal wire having a circular cross-section arranged in each of saidgrooves, at least one flexible, insulating member in each of saidgrooves, said member extending along a plane surface of said strip inthe direction of length thereof.

and in said grooves and under said successve circular wires, an nsulatngadhesive for connectng said circular wres and said insulatng member attl1eir ponts of engagement, and one end of each of said wires ccnsistingof a base metal provded with a surface of precious metal.

References Cited in the file of ths patent UNITED STATES PATENTS HarveySept. 26, 1950 Fritts Dec. 19, 1950

